1. Field of the Invention
This invention relates to an acoustic vibration sheet and a polypropylene composition for the same.
More particularly, it relates to an acoustic vibration sheet such as a speaker cone having improved acoustic characteristic, adhesion and high-impact strength and a polypropylene composition for the same.
2. Description of the Related Art
It has been known that polypropylene resins represented by polypropylene and compositions thereof are useful for acoustic vibration sheets.
For example, Japanese patent application laid-open Nos. Sho57-154994/1982 and Sho58-3499/1983 are directed to a product obtained by blending a definite quantity of mica having a specified shape with polypropylene or a copolymer of propylene with another monomer to make these material composite, whereby a considerably large effectiveness is observed.
However, acoustic vibration sheets produced from such compositions are still insufficient in the acoustic characteristic, adhesion and the high-impact strength thereof. An acoustic vibration sheet is disclosed in U.S. Pat. No. 4,190,746 which is a product obtained by laminating or coating low density polyethylene or non-crystalline polypropylene onto a sheet of general-purpose polypropylene or propylene copolymer. However, such a product is not satisfactory in the acoustic characteristic and adhesion thereof are still insufficient.